1. Field Of The Invention
The present invention relates to a method for producing a polyphenylene ether. More particularly, the present invention is concerned with a novel method in which oxidative coupling of a phenol compound is effected in a reaction medium containing methanol and or ethanol in the presence of a highly active catalyst having an improved water resistance which is comprised of at least one copper compound, at least one 1,3-diamine compound and at least one halogen compound. The novel method can be advantageously employed for producing a polyphenylene ether which has a desirable color and gives a composition improved with respect to Izod impact strength in combination with a rubber-reinforced polystyrene and the like. Major application of such a composition is found in the field of generally known engineering plastics.
2. Discussion Of Related Art
It was proposed in U.K. Pat. No. 930,993 to use a copper compound in combination with a member selected from various amines as a polymerization catalyst in the method for the production of a polyphenylene ether in which oxidative coupling of a phenol compound was conducted. Since then, a number of proposals have been made to provide an improved process by the use of a specific species of copper compound, by the use of combination of a copper compound with a halogen compound, or by the use of a specific amine, e.g. a primary, secondary or tertiary amine, a monoamine or a di- or polyamine.
For example, U.S. Pat. Nos. 3,306,875, 3,344,116 and 3,432,466 disclose a catalyst for producing a polyphenylene ether which comprises a copper compound and a tetraalkyldiamine, e.g. N,N,N',N'-tetramethyl-1,3-butanediamine. Further, U.S. Pat. No. 3,989,671 discloses a catalyst for producing a polyphenylene ether which comprises a copper compound, a tetraalkyldiamine and an iodine compound. The catalysts disclosed in these publications, however, do not have a desirably high catalytic activity.
Recently, U.K. Pat. No. 1,497,293 discloses that a copper amine complex, e.g. a complex comprised of a copper ion, a bromide ion, N,N'-di-t-butyl-ethylenediamine and a tertiary amine, e.g. N-methylpyrrolidine, has a somewhat improved catalytic activity in a process for producing a polyphenylene ether. It has become apparent, however, that the polyphenylene ether as produced using the above-mentioned catalyst has an undesirable color and, when it is combined with a styrene resin, e.g. rubber-modified polystyrene, it gives a composition having a poor impact resistance and a poor thermal stability. To cope with this problem, the use of such a complex catalyst in combination with a secondary monoamine, e.g. di-n-butylamine, has been proposed as disclosed in U.S. Pat. No. 4,092,294. Further, the use of such a complex catalyst in combination with a bromide ion is disclosed in European Pat. No. 103,154 in which the ratio of the bromide ion to a phenol compound to be coupled is at least 1:35. Moreover, in order to overcome the problem, the use of such a complex catalyst characterized by the employment of a mixture of a cuprous salt and a cupric salt as a copper source has been proposed as disclosed in European Pat. No. 111,722, and that characterized by the employment of a dimethylamine as a secondary monoamine has been proposed as disclosed in U.S. Pat. No. 4,477,651.
The catalytic activities of the conventional catalysts are not satisfactory, especially in a continuous process for the polymerization of a polyphenylene ether. This is partly attributable to the consumption of an amine component, e.g. N,N'-di-t-butylethylenediamine, during the polymerization step of a phenol compound. In this connection, reference may be made to U.S. Pat. No. 4,471,068. Further, it is to be noted that all of the known catalysts as set forth above have a serious drawback in that their catalytic activity is disadvantageously decreased by the action of the water formed during the oxidative coupling of a phenol compound. It is believed that the water causes a component or components of the catalyst to be hydrolyzed and also causes a metal component of the catalyst to be changed to an inactive state in the oxidative coupling of a phenol compound, leading to a lowering in the catalytic activity of the known catalysts.